The present invention relates to an apparatus and method for increasing the traction of a wheel supported land vehicle, such as an automobile, especially handling-oriented sports cars.
There are currently several widely known systems of increasing the loading, usually known as downforce, on the wheel assemblies of a vehicle to improve traction without significantly increasing the total vehicle mass. Nearly all fall into one of the following categories: 1) wings oriented to generate downforce attached directly to unsprung suspension components; 2) wings or vacuum generating tunnels attached to a sprung portion of the vehicle, usually the frame or body; and 3) mechanical vacuum generating devices attached to a sprung portion of the vehicle, usually the frame or body. Although any of these can increase the wheel loads by a factor of three or more, they each have significant disadvantages.
Systems of the first category typically require large wings on tall spars to generate significant downforce. This often requires that the wings be in clean air flow to operate effectively and, thus, must be located away from the body of the vehicle. This significantly increases the size of the vehicle. Systems of the first category also tend to obstruct operator vision. They also tend to be fragile and to fail structurally in service.
Systems of the second category can negatively impact the vehicle operation, because the suspension must be designed to accommodate the normal loads of the vehicle as well as the load generated by the downforce devices. Thus, the normal operation of the suspension, which consists of stabilizing and/or isolating the vehicle from linear acceleration loads, lateral acceleration loads and road irregularities, is compromised. In addition, if wings or spoilers are significant downforce generators, then they are usually large enough to obstruct driver vision or significantly increase the size of the vehicle. If tunnels or other aerodynamic arrangements are used to generate a vacuum, and as such are significant downforce generators, then they require significant and precise profiling of the underside of the vehicle, especially with respect to the clearance between the vehicle and the road surface. This causes a double compromise in the suspension design, since the suspension must both accommodate the increased loading and maintain a relatively low and consistent ride height. This usually causes both the aforementioned problem of compromised suspension operation and unacceptably limited ground clearance. Furthermore, profiling takes up significant space within the vehicle and compromises the location of other major components.
Systems of the third category suffer from the aforementioned additional sprung loading and limited ground clearance problems of the second category.
The traction enhancement system of the present invention increases the traction of a wheel-supported land vehicle by applying areas of vaccuum directed toward the road surface at or near one or more, even all, of the wheel assemblies in order to significantly increase the load on each wheel and thus maximize the traction while not significantly increasing the vehicle mass. The load increase is generated by a vacuum intake horn facing the road surface. The vacuum intake horn for the vacuum is in constant contact and moves proportionally or exactly with a portion of the vehicle that is at least partially unsprung. More specifically, the vacuum intake horn is fixed to the vehicle at the wheel assembly or some point between the wheel assembly and articulation points of the suspension with the vehicle chassis, and hence is at least partially, if not fully, unsprung.
The vacuum intake horn is primarily attached to a portion of the vehicle that is at least partially unsprung and thus primarily loads the unsprung members of the vehicle, especially the wheel assembly, thereby enabling the majority of the vehicle to ride on a suspension that is less compromised than it would be if the vacuum intake horn were attached to a fully sprung portion of the vehicle. Each vacuum intake horn is located near a wheel assembly and the road surface, which permits the system of the present invention to be more firmly attached than unsprung wings used to enhance traction. The vacuum intake horn creates more downforce as a result of being able to be positioned with significantly reduced clearance above the road surface. The clearance of the vacuum intake horn of the present invention is primarily affected by deflection of the wheel assembly, which is comprised almost entirely of deflection in the tire and is usually only a fraction of the deflection in the vehicle suspension. Therefore, the clearance of the vacuum intake horn of the present invention above the road surface can be substantially more consistent than vacuum devices associated with sprung portions of a vehicle. The clearance of such sprung vacuum devices is affected by both the wheel assembly deflection and the suspension deflection. The system of the present invention allows more vacuum and greater downforce per unit area to be generated, and much greater latitude in the location and method of vacuum generation because the downforce is not necessarily created by the specific aerodynamics of the vehicle. The method of providing a vacuum in the vacuum intake horn and the location of the vacuum generating device are not critical to the operation of the system.
The vacuum intake horn is attached to the vehicle at a point such that the vacuum intake horn experiences no more than 75% of the spring deflection experienced by the vehicle chassis, which is fully sprung and experiences all of the spring deflection of the vehicle suspension. In other words, the vacuum intake horn is attached to the vehicle at a point such that movement of the vacuum intake horn relative to its associated wheel assembly is no more than 75% of the movement of the vehicle chassis relative to that wheel assembly. Attachment to the wheel assembly allows the vacuum intake horn to avoid all of the motion of the vehicle chassis relative to the wheel assembly. Other points of attachment that cause the vacuum intake horn to have no more than 75% of the movement of the vehicle chassis relative to the wheel assembly can be determined without undue experimentation.
The term xe2x80x9cunsprungxe2x80x9d refers to any part of a vehicle whose load is not fully carried by the damping devices of the suspension, unsprung parts being tire/wheel assemblies, hub/spindle assemblies, control arms, stabilizing linkages, brakes, half shafts, springs and shocks. xe2x80x9cFully unsprungxe2x80x9d refers to parts whose load is carried solely by the tire/wheel assemblies. Typically, these include hub/spindle assemblies, brakes, tires and wheels. xe2x80x9cPartially unsprungxe2x80x9d refers to parts whose load is only partially carried by the damping devices of the suspension and which have some portion of their load carried by the tire/wheel assemblies. These are generally components of the suspension itself and half shafts. To be fully sprung, a part""s entire load must be carried through the damping devices. Fully sprung parts include parts that are completely supported on a side of the points of attachment of the vehicle chassis or frame to the suspension that is opposite to the side on which the tire/wheel assemblies lie.
The traction enhancement system of the present invention preferably has an arrangement which compensates for deflection in the tires. The compensating arrangement reduces the variation in ground clearance of the vacuum intake horn from, for example, 2.0 inches, if the vacuum intake horn is rigidly attached to the tire/wheel assembly, to 0.6 inches. The system always maintains some ground clearance, but a flexible skirt around the vacuum intake horn face can allow for some interference with the ground. The compensating arrangement can include a mechanism for retracting the vacuum intake horn while the vacuum intake horn is inoperative. In both the operative position and the inoperative position, as much of the intake horn as possible is positioned behind the wheel, with respect to the direction of movement of the vehicle, so that the wheel blocks road debris and the like from striking the intake horn. Preferably, all of the horn is behind and within the lateral outline of the wheel and tire.
The compensating arrangement is attached to the vehicle at a point of attachment primarily through, for example, an attachment yoke connected to an unsprung hub assembly of the vehicle both at the upper and lower suspension attachment points. A secondary attachment point of the compensating arrangement is through a mounting bracket attached to the chassis of the vehicle, which is fully sprung.
The operation of the system is based on the spring rates of the tires and the suspension. The tires and the suspension each have a spring rate which proportionally correlates a given deflection with a particular load. As a load varies at a given wheel position, there is a deflection in the suspension that changes the angle of the control rod and the main beam, each of which is pivotally attached to the support beam. A difference between the length of the main beam and the length of the control rod has the effect that a change in the angle of the main beam and the control rod changes the angle of a support beam. The change in the support beam angle produces a change in the vacuum intake horn face vertical position relative to the hub/spindle assembly that is inverse and nearly equal to the change in hub/spindle assembly position relative to the road surface caused by tire deflection, thus maintaining a more consistent clearance between the face and the road surface. A similar relation between the support beam and the leveling link controls the intake horn face angle. The change in angle of the main beam causes a change in the horizontal distance between the main beam pivot and yoke pivot requiring that an arrangement, such as a soft mount be provided to let the mounting block slightly move horizontally. In the illustrated case, 0.3 inches of tolerance is required.
In the illustrated example, the spring rates are estimated to be 1000 lbf.(pounds force)/in. for each tire and 200 lbf./in for the suspension. These are fairly typical values for normal automobiles. Different spring rates would require adjustments in the position of the pivots, such as by changing the location of the attachment of the control rod to the support beam, moving the location down when the differences are proportionally smaller and up if larger. Changing the leveling rod position on the main beam is one way to adjust the face angle. Varying the lengths of the support beam and leveling rod the preferred way to control the average ground clearance.
Traction enhancement devices, including those according to the present invention, tend to cause drag and increase the power requirements for forward motion when operating and thus reduce the top speed, slow the vehicle, or cause greater fuel consumption. Therefore, the operation of the system of the present invention is often limited to periods when increased traction is necessary, such as stopping or extreme cornering. The system is deactivated during periods when enhanced traction is usually not required such as maximum speed operation, cruising or forward acceleration.